The invention is directed to a method of making molecular sieve that contain metals, catalysts containing molecular sieves that contain metals, and a method for converting an oxygenate feedstock to a product, including olefin. In particular, the invention is directed to a silicoaluminophosphate catalyst with a molecular sieve surface that is heat impregnated with a metal.
Olefins, particularly light olefins, have been traditionally produced from petroleum feedstocks by either catalytic or steam cracking. Oxygenates, however, are becoming an alternative feedstock for making light olefins, particularly ethylene and propylene. Promising oxygenate feedstocks are alcohols, such as methanol and ethanol, dimethyl ether, methyl ethyl ether, diethyl ether, dimethyl carbonate, and methyl formate. Many of these oxygenates can be produced from a variety of sources including synthesis gas derived from natural gas; petroleum liquids; and carbonaceous materials, including coal. Because of the relatively low-cost of these sources, alcohol, alcohol derivatives, and other oxygenates have promise as an economical, non-petroleum source for light olefin production.
One way of producing olefins is by the catalytic conversion of methanol using a silicoaluminophosphate (SAPO) molecular sieve catalyst. For example, U.S. Pat. No. 4,499,327 to Kaiser, discloses making olefins from methanol using a variety of SAPO molecular sieve catalysts. The process can be carried out at a temperature between 300xc2x0 C. and 500xc2x0 C., a pressure between 0.1 atmosphere to 100 atmospheres, and a weight hourly space velocity (WHSV) of between 0.1 and 40 hrxe2x88x921.
Inui has shown that nickel substitution into the SAPO-34 framework results in an increase of ethylene selectivity relative to unsubstituted SAPO-34. J Chemical Society Chem. Commun. p.205, 1990. For example, at 450xc2x0 C. the product stream comprised 88% ethylene and 5% propylene (100% methanol conversion).
In contrast to the work of Kaiser and Inui, metal incorporation may also take place post-synthesis, that is, following the synthesis of the molecular sieve framework. For example, U.S. Pat. No. 5,962,762 to Sun et al. teaches a process for converting methanol to light olefins using a metal-incorporated SAPO catalyst. An aqueous metal solution, preferably a nickel or cobalt containing solution, was adsorbed onto the SAPO molecular sieve by allowing the solution to remain in contact with the SAPO overnight at ambient conditions. The treated molecular sieve was then separated from the solution and dried. U. S. Pat. Nos. 5,625,104 and 5,849,968 to Beck at al. teach a process of incorporating alkali earth and alkaline earth metals into a zeolitic catalyst by pretreating the zeolite with an organosilicon or poly-oxo silicon compound followed by the treatment of a metal solution. U.S. Pat. No. 4,692,424 to Le Van Mao teaches a process for the dry incorporation of manganese ions on the external reactive sites of ZSM catalysts by adding a minimum amount of an aqueous manganese solution to form a malleable paste and extruding the paste under pressure.
In spite of the prior efforts to modify molecular sieve, the need to find a molecular sieve or molecular sieve catalyst that exhibits high ethylene and/or propylene selectivity still exists. Otherwise, the use of crude oil feedstock to produce these olefins will continue to be economically favored.
This invention provides various compositions of a molecular sieve having a surface heat impregnated with one or more metals and of a method of making the same. The metals are selected from Group IIA metals, Group IHA metals, Group IB metals, Group 111 metals, Group 111 metals, Group VIB metals, Group VB metals, Group VIIB metals, Group VIIIB metals, Group VI11B metals, and mixtures thereof.
In one embodiment, the metals are selected from aluminum, magnesium, calcium, barium, lanthanum, titanium, chromium, iron, cobalt, nickel, copper, zinc, and mixtures thereof The silicoaluminophosphate (SAPO) molecular sieve will contain about 0.5 to 40 percent by weight, preferably about 1 to 20 percent by weight, most preferably 1 to 10 percent by weight, of the metal. In the preferred embodiment, the SAPO molecular sieve will have a surface heat impregnated with copper, zinc, or a mixture thereof, wherein the copper and/or zinc will be present in about 1 to 20 percent by weight. The metal disposed on the SAPO molecular sieve is a heat decomposition product of a metal acetate, metal nitrate, metal sulfate, or metal halide. The surface is heat impregnated with the metal at a temperature from 30xc2x0 C. to 400xc2x0 C., preferably from 120xc2x0 C. to 260xc2x0 C., most preferably from 160xc2x0 C. to 220xc2x0 C. The SAPO molecular sieve is selected from SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAP047, SAPO-56, the metal containing forms thereof, and mixtures thereof, more preferably, SAPO-18, SAPO-34, SAPO-35, SAPO-44, SAPO-47, and mixtures thereof, most preferably, SAPO-34A, SAPO-34B, and mixtures thereof.
The invention is also directed to a SAPO molecular sieve catalyst comprising: a surface heat impregnated with a metal selected from the group consisting of Group IIA metals, Group IHA metals, Group IB metals, Group IIB metals, Group IIIB metals, Group VIB metals, Group VB metals, Group VIB metals, Group VIIB metals, Group VIIIB metals, and mixtures thereof; and a binder. Generally, the binder is selected from alumina, aluminum chlorhydrol, clay, and mixtures thereof.
In one embodiment, the metals are selected from aluminum, magnesium, calcium, barium, lanthanum, titanium, chromium, iron, cobalt, nickel, copper, zinc, and mixtures thereof. The SAPO molecular sieve will have about 0.5 to 40 percent by weight, preferably about 1 to 20 percent by weight, most preferably 1 to 10 percent by weight, of the metal. In the preferred embodiment, the SAPO molecular sieve will have a surface heat impregnated with copper, zinc, or a mixture thereof, wherein the copper and/or zinc will be present in about 1 to 20 percent by weight. The metal disposed on the SAPO molecular sieve is a heat decomposition product of a metal acetate, metal nitrate, metal sulfate, or metal halide. The surface is heat impregnated with the metal at a temperature from 30xc2x0 C. to 400xc2x0 C., preferably from 120xc2x0 C. to 260xc2x0 C., most preferably from 160xc2x0 C. to 220xc2x0 C. The SAPO molecular sieve is selected from SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, the metal containing forms thereof, and mixtures thereof, more preferably, SAPO-18, SAPO-34, SAPO-35, SAPO-44, SAPO-47, and mixtures thereof, most preferably, SAPO-34A, SAPO-34B, and mixtures thereof.
The invention is also directed to a method of making a molecular sieve comprising: mixing a metal containing solution with a SAPO molecular sieve, wherein the SAPO molecular sieve contains a template; heating the mixture to a temperature between 30xc2x0 C. and 400xc2x0 C. to obtain a SAPO molecular sieve having a surface heat impregnated with a metal; separating the heated SAPO molecular sieve from the heated metal containing solution; and calcining the separated SAPO molecular sieve. The metal is selected from the group consisting of Group IIA metals, Group IIA metals, Group IB metals, Group IIB metals, Group IIIB metals, Group VIB metals, Group VB metals, Group VIB metals, Group VIIB metals, Group VIIIB metals, and mixtures thereof In one embodiment, the metal is selected from aluminum, magnesium, calcium, barium, lanthanum, titanium, chromium, iron, cobalt, nickel, copper, zinc, and mixtures thereof, more preferably copper, zinc, or a mixture thereof The source of the metal is the heat decomposition product of the metal containing solution. In one embodiment, selected metal salts include acetates, nitrates, sulfates, halides, and mixtures thereof, more preferably nitrates. The metal containing solution comprises a metal concentration between 0.01 M and 1.0 M, preferably between 0.05 M and 0.5 M, more preferably between 0.08 M and 0.3 M. The surface heat impregnated with the metal is heat impregnated at a temperature from 30xc2x0 C. to 400xc2x0 C., preferably from 120xc2x0 C. to 260xc2x0 C., more preferably from 160xc2x0 C. to 220xc2x0 C., at autogeneous pressure.
The invention is also directed to a method of making an olefin from an oxygenate feedstock comprising: providing a catalyst comprising a SAPO molecular sieve having a surface heat impregnated with a metal selected from the group consisting of Group IIA metals, Group IHA metals, Group IB metals, Group IIB metals, Group IIIB metals, Group VIB metals, Group VB metals, Group VIB metals, Group VIIB metals, Group VIIIB metals, mixtures thereof, and a binder; and contacting the oxygenate feedstock with the catalyst.
In one embodiment, the SAPO molecular sieve is selected from SAPO-18, SAPO-34, SAPO-35, SAPO-44, SAPO47, and mixtures thereof In the preferred embodiment, the SAPO molecular sieve has a surface heat impregnated with a metal comprising copper, zinc, or a mixture thereof. The copper, zinc, or a mixture thereof is present in the molecular sieve in about 1 to 20 percent by weight. The preferred oxygenate feedstock will comprise methanol.